The present invention relates to an apparatus for processing a substrate for applying a photolithographic process to a substrate such as a semiconductor wafer or a glass substrate for a liquid crystal display (LCD) device.
In a manufacturing process of the semiconductor device, photolithography is used. For example, the photolithographic process for manufacturing an LSI includes the steps of coating a resist on a semiconductor wafer, exposing the coated wafer to light, and developing it. Of the steps, the resist coating step and the developing step are performed by using a substrate processing apparatus disclosed in U.S. Pat. Nos. 5,664,254 or 5,826,129.
The conventional apparatuses described in these publications in the prior art have a process station for processing a plurality of wafers simultaneously in parallel. The process station has a plurality of multi-layered process unit groups and a main transfer arm mechanism. The main transfer arm mechanism has a holder capable of holding at least two wafers at the same time and a back-and-forth moving mechanism for moving the holder, an up-and-down moving mechanism for moving the holder in a Z-axis direction, and a .theta.-rotation driving mechanism for rotating the holder around the Z-axis. The multi-layered process unit groups are arranged so as to surround the main transfer arm mechanism. The main transfer arm mechanism transfers a wafer W to a coating unit, a developing unit, and a thermal process unit, sequentially. The wafer W is coated, baked, cooled and developed in the individual units.
In recent years, with a high integration and enlargement in wafer size, it has taken a longer time for manufacturing and inspecting the device than before. It has therefore been strongly desired to further increase a throughput of the photolithographic process. However, since a chemically amplified resist is usually exposed to a KrF excimer laser, which is weak in light intensity, time required for a developing process for the resist is longer than other treatment processes. Furthermore, time required for the resist coating is increased as the wafer increases in diameter.
To satisfy the desire to increase the throughput, if the number of the development units and coating units is increased by connecting a plurality of process stations to each other via a transfer unit, it is possible to improve the throughput in the time-consuming developing process and coating process and simultaneously to reduce stand-by time for the wafer in the developing and resist-coating processes.
However, if the number of the process stations is increased, time required for transferring the wafer between the process stations increases. More specifically, the wafer is transferred by a main transfer arm mechanism of a process station from the process station to a transfer unit, and further transferred to another process station from the transfer unit by another main transfer arm mechanism. As described, since the wafer is transferred between two main transfer arm mechanisms via the transfer unit, it takes too much time to transfer the wafer W, with the result that a throughput decreases.
Furthermore, if the wafer is transferred to the vertically-stacked four coating units or developing units by a single main transfer arm mechanism, an excessive load is applied to the single main transfer arm mechanism. As a result, the wafer cannot be smoothly transferred. To reduce the up-and-down moving amount of the main transfer arm mechanism (to reduce the load), it may be possible that two coating unit groups or two developing unit groups, each group being stacked in two stages, are arranged side by side and the wafer is transferred to four coating units or four developing units by a single main transfer arm mechanism. However, such an arrangement of the coating units or the developing units increases the footprint.